FIG. 1 illustrates an exemplary disk drive system 10, including a hard disk controller (HDC) 12 that interfaces with a read/write channel (R/W channel) 14. The R/W channel 14 may be in communication with a media 16 (e.g., a disk). Data transfer between HDC 12 and the R/W channel 14 may be synchronized by a number of control signals, e.g., read gate (RGATE) and write gate (WGATE) control signals. In a read operation, R/W channel 14 may process an incoming signal from media 16 and transfer the data to HDC 12. In a write operation, data may be transferred from HDC 12 to the R/W channel 14 to be written to the media 16.
In various embodiments, latency may refer to the time or byte delay that data remains in the R/W channel. For example, some disk drive systems may have latencies of about 20 bytes which, depending on the particular system, may amount to a time delay of between about 800 nanoseconds (ns) and 5 milliseconds (ms).
Technology such as iterative coding (e.g., turbo coding, low-density parity-check coding (LDPC coding), etc.), which is being introduced into modern disk drive systems, may involve more processing before the data is available. That is, the latency within which the R/W channels encode and decode may be relatively longer, and hence, it may be desired that the R/W channels tolerate relatively higher latencies.
In the last few years, R/W channels have been developed that may tolerate relatively higher latencies. In addition, long latency protocols have also been developed.
In some of the long latency protocols, the R/W channel may not know in advance the number of symbols to be written to the media for a corresponding WGATE high signal. In various embodiments, the R/W channel may have to count the number of symbols between a falling edge of the WGATE signal and a falling edge of another appropriate control signal to ascertain the number of symbols to be written to the media (or the number of symbols to be read back from the media) for an assertion of the WGATE signal.